Large scale high temperature reaction furnaces are used in a variety of industrial applications including initial H2S combustion and ammonia destruction in Claus sulfur recovery units in oil refineries and gas plants, elemental sulfur combustion in the first process stage in sulfuric acid plants, decomposition of spent sulfuric acid in spent acid regeneration facilities, and other types of thermal oxidizers.
These reaction furnaces are typically refractory-lined cylinders with inside diameters ranging in size from 3 feet to diameters in excess of 20 feet, with furnace lengths ranging from 20 feet to over 100 feet long. The furnaces are configured with a large process burner at one end that discharges into a waste heat recovery boiler at the other end. The normal operating temperatures of these reaction furnaces range from 1800° F. to temperatures in excess of 3000° F., driving the need for a stable, reliable refractory lining.
The unit may have a refractory ceramic checkerwall or choke ring located part of the way down the length of the reaction furnace which, in part, functions to create two distinct reaction zones, each having its own environment and chemistry. This partition wall must be made of a refractory material because of the operating temperatures and chemistry involved in these reactions. The ability to partition reactions using these structures gives chemical engineers the ability to significantly improve the process by staging the reactions.
For example, Claus sulfur recovery units, which were originally designed to convert hydrogen sulfide generated in upstream processes to elemental sulfur, can also be used to treat effluent gas from sour water stripper units which contain ammonia. Ammonia is destroyed most effectively at the higher temperatures which can be created in the reaction furnace stage of the Claus sulfur recovery unit. By staging the process within the reaction furnace, by holding some of the hydrogen sulfide back for secondary injection part way down the combustion chamber, typically after the checkerwall or choke ring, a higher temperature is achieved just downstream of the burner since there is less hydrogen sulfide to heat up. The ammonia is more effectively destroyed at the higher temperatures, and the balance of the hydrogen sulfide is injected and converted further downstream.
Another example of staged combustion is found in decomposition furnaces used in spent acid regeneration processes. In this instance, the process is staged by holding back some of the combustion air, effectively reducing the peak process temperature immediately after the burner. Lowering this temperature reduces the generation of environmentally harmful NOx in the process stream. Secondary air is injected downstream of a baffle wall to complete the combustion process with the remaining spent acid.
Applicant provides a special, high reliability partition wall, also referred to as a checkerwall/bafflewall in U.S. Pat. No. 5,954,121, the entirety of which is incorporated herein, that is effectively used in these types of high temperature reaction furnaces. This partition wall design is based on the use of a plurality of stacked, precision-shaped hexagonal refractory blocks (also referred to herein as hexagonal blocks or hexblocks). For example, FIG. 1 show a hexagonal block 1 that is 8-9 inches deep (long) and has a hexagonal outer shape along the full depth (i.e., the entire longitudinal extension length) thereof, and a hexagonal cross-sectional shape. The hexagonal blocks 1 each include an engaging tongue-and-groove system, including tabs t and grooves g that interlock with one another in adjacent blocks when stacked to provide a secure and reliable array assembly (partition wall) 13, as shown in FIG. 2.
In addition, Applicant also provides vector tiles 11 that can be installed in conjunction with the hexagonal blocks 1 in a partition wall configuration or array in order to control or to direct the flow of process gas downstream of the partition wall. This partition wall configuration 14, which is shown in FIG. 3, is also referred to as a VECTORWALL™ configuration, as described in U.S. Pat. No. 8,439,102, the entirety of which is incorporated herein. Furthermore, in another type of configuration, a plurality of blocking tiles 12 can be installed in some of the hexagonal blocks 1 to restrict flow through predetermined portions of the partition wall assembly to define a bafflewall 15 (see, e.g., FIG. 4).
In the staged reaction process, the effectiveness of how well the secondary injected gas or air is distributed and mixed in the process stream governs the conversion effectiveness for the secondary flow, and, in turn, the overall conversion effectiveness of the entire chamber. Typically, these secondary injections are made at discreet single injection points, which insert the secondary gas into the process flow. Prior to the present invention, the secondary injection of process gas or air was simply conveyed into the reaction chamber through simple ports located just downstream of the checkerwall structure 13 (see, e.g., FIG. 5) or, in the case of an overflow bafflewall, just at the overflow area of the baffle wall, as discussed above. These ports may or may not be configured with a nozzle to meter or otherwise somewhat control the injection and secondary flow, as dictated by the process considerations. Typically, however, a single injection point of this type does not efficiently distribute the secondary flow throughout the overall flow field in order to achieve optimal results.
The importance of controlling the distribution of this secondary flow with respect to completing the intended reactions within the reaction chamber volume is important, and there exists a significant need for improving the uniformity of the distribution of the secondary injected gas in such reaction furnaces, thereby improving the mixing effectiveness downstream.